Meanwhile, Syria's antiquities director, Maamoun Abdelkarim, on Thursday told the BBC IS -- also identified as Daesh and the acronyms ISIS and ISIL -- also destroyed a 2,000-year-old statue of a 10-foot tall lion in Palmyra.

He said the destruction of the Lion of al-Lat is "the most serious crime [IS has] committed against Palmyra's heritage."

It's unclear if the smaller sculptures were fake, SOHR said, because it is believed IS has sold authentic antiquities to neighboring countries to raise funds.

UNESCO Director-General Irina Bokova on Thursday said it was difficult for officials to investigate claims of the illegal trade of antiquities. She called on the U.N. Security Council "to share any relevant intelligence they may have in this regard, to help counter these criminal activities.

"It is said you can't fight an enemy you don't know -- this is why we need more research and better analysis," Bokova said, calling for assistance from British think tank RUSI.

Bokova's plea came one day after UNESCO said it will use satellites to monitor and protect threatened ancient archaeological sites. IS has destroyed mausoleums, temples and statues around the area on a wide scale, and planted explosives within Palmyra. It previously destroyed Assyrian ruins and artifacts in Syria.

Bokova called the practice of destroying artifacts and archaeological sites a "cultural cleansing."